Looking for opinions on my electrically dependent main power distribution concept. RV8, VFR mission, single alternator, aft mounted batteries, dual-boost pumps, ignitions, and ECU's. Battery 2 functions as a brown out battery and additional endurance. No interest in an E bus simply turn off one or both batteries and land. No interest in using battery 2 for engine start.
While the two battery bus scheme addresses your very electrically dependent engine, I offer you could get more out of them.
- The diode isolation between the batteries on the output side of the master solenoids provides no real function.
- If you run both batteries in parrellel you then eliminate the previously mentioned voltage drop for charging the second battery, and you also get both batteries for engine start. I know you said that you were not interested in this but why not?
- If you do run both batteries in parallel by connecting the output of the two master solenoids, you gain the option to have all your ?non-panel? stuff powered from this common connection (engine start, landing lights, pitot heat, strobes, etc.). Now power your two main panel busses from small relays connected to each battery. This reduces the drain form the master solenoids if you lose the alternator. On my planes the immediate action for loss of alternator is to open both master solenoids to dump the ?not needed for continued IFR flight? loads.
In my first RV-8A I mounted two PC-625 batteries behind the firewall on the forward section floor, one on each side. For the new RV-8 project I will mount one on the right side aft of the firewall, and one in the normal location aft of the baggage compartment. Running the W&B numbers from a buddy?s similarly equipped RV-8 the one battery aft will address my normal solo flying conditions.
One other consideration, battery health. For electrically dependent airplanes you need to have confidence that the designed reserve capacity is actually there. This means:
- If you run a battery flat, consider it dead and replace it. This also mean your don?t jump start the engine and fly off into the blue.
- You decide your maintenance routine for battery replacement. Starting out with an externally dependent electronic igntion set up, I replaced one of the two batteries every two years - so no battery was more than four years old. Replacing this first problematic ignition with pMags I eliminated this design weakness and set replacement at one every three years to support my 100% electrically dependent panel.
Carl